1. Field of Invention
The present invention relates to a source driver. More particularly, the present invention relates to a digital to analog converter of the source driver.
2. Description of Related Art
A liquid crystal display (LCD) has many advantages over other types of displays, and is widely used in various applications such as televisions, mobile phones, video camcorders, personal computers and so on. Image data of the LCD are provided through one or more source drivers.
FIG. 1 shows a diagram of the conventional source driver of the LCD. The source driver 100 includes the channels 108, the multiplexer 112, the output pads 114, the switch 120, and the data bus 118. The channel 108 is connected to the output pads 114 via the multiplexer 112, in which the switch 120 re-distribute the charges on the output pads 114 when the source driver powers off. Each channel 108 has a shift register 122, a latch unit 133, a level shifter 128 and a digital-to-analog converter (DAC) 130. Each latch unit 133 includes a first latch 124 and a second latch 126 connected in series.
The digital pixel data on the data bus 118 is stored in the latch units 133, and moreover, the digital pixel data is stored first in the first latch 124 and then stored in the second latch 126. The DAC 130 receives the level-shifted digital pixel data and generates driving voltage based on the level-shifted digital pixel data.
However, due to the process variation, the DACs of the channels in the same source driver may generate different analog gamma voltages even if they receive the same level-shifted digital pixel data. As a result, the source drivers may generate different driving voltages even if they receive the same level-shifted digital pixel data, which causes the image noise (band mura) on the display.
Therefore, there is a need for a source driver with improved digital to analog converters to reduce the display image noise.